1. Field of the Invention
The present invention relates to improvements in and relating to the current limiting circuit portion of a chopper control system connected to a load having inductance such as a DC motor.
2. Description of the Prior Art
In a known type of chopper control system, the main current flowing through a DC power source, a main circuit switch, a load and a chopper circuit whose duty cycle is controlled by an on-pulse oscillator circuit and an off-pulse oscillator circuit, is detected by a resistor connected in series with these elements so that when the detected output reaches a predetermined value, a current limiting circuit is brought into operation to act on the off-pulse oscillator circuit and the duty cycle of the chopper circuit is restrained to prevent the main current from exceeding the predetermined value.
With the conventional system of the above-mentioned construction, however, it is essential to use a main current detecting resistor inserted in series in the main circuit so that the use of a detecting resistor with a high resistance value results in a loss of the main power, whereas the use of a detecting resistor having a low resistance value causes the current limiting circuit to operate erroneously due to a noise signal. Thus, there is a disadvantage that the types of resistor which can be used for such detecting resistor are limited with the resulting increase in costs, increased space required for mounting a large detecting resistor and so on.